Friction disc and method for making a lining forming it

ABSTRACT

The friction disk ( 24 ) includes a support web ( 28 ) the outer peripheral portion ( 40 ) of which is sub-divided into radial blades ( 42 ) offset axially from the central fixing part ( 44 ) with respect to the general plane of the web ( 28 ), and including friction linings ( 30, 32 ) on either side of the peripheral portion ( 40 ), each lining ( 30, 32 ) including, on the one hand, a fixing surface ( 64, 66 ) a fixing area ( 62 ) of which is fixed onto at least one central part ( 44 ) of a radial blade ( 42 ), and, on the other hand, a reduced-thickness area ( 72 ), in an area separate from the fixing areas ( 62 ); at least one reinforcing element ( 74 ) extends face-to-face with at least a part of a reduced-thickness area. 
     The invention also proposes a method of manufacturing a friction lining ( 30, 32 ) of the type described above.

TECHNICAL FIELD OF THE INVENTION

The invention proposes a friction disk, especially for a motor-vehicledry clutch.

The invention more particularly proposes a friction disk, especially adry-clutch friction disk for a motor vehicle.

STATE OF THE ART

In a known way, the friction disk includes a support web in the form ofan annular washer, the outer peripheral portion of which is subdividedinto radial blades which, by virtue of folds, feature a central fixingpart which is connected to the central portion of the web by atangential fold which forms the foot of the blade and which isperpendicular.

The tangential fold allows an axial offset of the central fixing partwith respect to the general plane of the central portion of the web.Friction linings are fixed on either side of the outer peripheralportion, for example by riveting or by bonding. Each friction liningcomprises an outer friction surface and an inner fixing surface, afixing area of which is fixed onto at least one lateral fixing face of acentral part of a radial blade which is offset axially towards the saidfriction lining.

Such a design is illustrated, for example, in the documentEP-A-0.579.554 (U.S. Pat. No. 5,452,783).

When such a friction disk is used for transmission of the rotationalmovement of the engine of a motor vehicle to the wheels, the centralportion of the web is linked to the primary shaft of a gearbox eitherdirectly or by way of elastic members.

When it is being used in a clutch device, the radial periphery of thefriction disk, especially the friction linings, is clamped axiallybetween a pressure plate and a reaction plate. The plates are driven inrotation by the engine flywheel. The axial offset of the central fixingpart of the blades with respect to the general plane of the centralportion of the web and the mechanism for linking to the clutch pedalmake it possible to obtain the application of the axial load, from azero value up to the rated value of this axial load which ischaracteristic of the setting of the clutch, during a part of themovement of the clutch pedal, which is the active clutch-engagementphase. During the active clutch-engagement phase, the two linings of thefriction disk approach one another over a distance calledprogressiveness travel. The graphical representation of the axial forceof the pressure plates on the friction as a function of the relativemovement of two linings under this force is called progressivenesscurve. At the end of the clutch-engagement phase, depending on thesetting and the characteristics of the clutch, the axial offset of thecentral fixing part of the blades with respect to the general plane ofthe central portion of the web may be practically cancelled out.

During the clutch-engagement phase, the axial clamping load istransmitted to the friction surfaces of the lining by the surfaces ofthe pressure and reaction action plates which are face-to-face.

The axial offset of the central fixing part of the blades is notcancelled out during this operating phase. The friction lining thereforebear essentially on the lateral fixing faces of the blades. Thedistribution of the pressures over the friction surfaces of the liningis therefore not uniform.

Moreover, at the start of the active clutch-engagement phase, therotational speeds of the engine flywheel and of the primary shaft of thegearbox are not homokinetic. This difference in rotation inducesfriction between the pressure plate and one of the linings, as well asbetween the reaction plate and the other lining.

The energy dissipated by the friction between the linings and thepressure and reaction plates, as well as the heating and the wearinduced on the linings, are increasing functions of the pressure betweenthe friction linings and the plates. Thus, during the clutch-engagementphase, the wear on the friction surfaces of the friction linings istherefore more rapid facing their fixing areas.

The areas of the fixing surfaces of the linings, which are not fixingareas and which are not in contact with the support web, are called freeareas, and they transmit a lower pressure in the course of the activeclutch-engagement phase and, consequently, wear out less rapidly.

Thus, the free areas of the linings are pushed back overall by theplates, and become thicker in step with the wear on the areas of thefriction surfaces facing the fixing areas.

Moreover, the high temperatures and stresses, especially in the areas ofthe friction surfaces facing the fixing areas, cause permanentdeformations, for example by the phenomenon of creep.

The cumulated effect of these deformations is called incrustation.

Incrustation is therefore manifested as an overthickness of frictionmaterial in the region of the free areas, protruding with respect to theplane passing through the inner fixing surfaces of the linings. Thisfriction material of the free areas, protruding, comes into contact withthe lateral faces of the blades which are opposite the lateral fixingfaces, during the active clutch-engagement phase, before theprogressiveness travel is terminated.

Whenever free areas are in contact with the peripheral part of the web,these free areas participate in the transmission of the axial forceexerted by the pressure and reaction plates, at a level equivalent tothe participation of the fixing areas.

In this case, if the differential in the rotational speeds between thetwo friction linings and the pressure and reaction plates is not zero,the speeds of wearing of the portions of the friction surfaces, on theone hand facing free areas in contact with the web, on the other handfacing fixing areas, are similar.

The greater the incrustation of the friction linings, the more the freeareas rapidly come into contact with the peripheral portion of the web,in the course of the active clutch-engagement phase.

When the rotational speeds of the engine flywheel and of the primaryshaft of the gearbox are homokinetic, there is no friction between thepressure and reaction plates, on the one hand, and the linings, on theother hand. The wearing of the linings does not change.

When the active clutch-engagement phase is terminated, if thedifferential in the rotational speeds between the two linings and thepressure plates is not zero, the clutch slips. The slipping of theclutch induces wear which diminishes the differences in thickness of thefree areas between the linings until the thicknesses of these free areasbecome uniform.

When the linings are not incrusted, the progressiveness curve of thefriction is a monotonic, increasing and continuous function. The slopeof this curve grows with the relative approach of the two linings, up toa finite value.

When the linings are incrusted, we can distinguish two periods. Thefirst period corresponds to the relative movement between two liningsfrom the free state until the first, thickest free area comes intocontact with the support web. The part of the progressiveness curvecorresponding to this first period remains monotonic, increasing andcontinuous. The second period corresponds to the residual application ofthe axial load transmitted by the pressure plates. The complementarypart of the progressiveness curve corresponding to this second periodcommences with a break point with a substantial augmentation of theslope. In general, the slope tends towards infinity towards the end ofthis second period. The progressiveness travel is reduced.

Incrustation therefore has a negative impact on the driving comfort ofthe vehicle during the clutch-engagement phase. This is because, duringthe passage from the first to the second period, the torque transmittedby the friction disk as a function of the axial force, that is to say ofthe axial movement of the pressure and reaction plates towards oneanother, varies abruptly.

The abrupt variation in transmission of the torque causes a jolt whichimpairs the driving comfort of the vehicle.

During the first period, the transmission of the torque is achieved inlarge measure by the areas of the outer friction surface of the liningsface-to-face with the fixing areas.

During the second period, the transmission of the torque is achieved bypractically all the outer friction surface of the linings.

OBJECT OF THE INVENTION

The present invention makes it possible particularly to increase theduration of use of the friction disk during which incrustation has nonegative impact on comfort, so as to increase the duration during whichthe driving comfort of the vehicle is optimal.

The invention thus makes it possible to even out the distribution of thepressures on the friction surfaces of the linings, which makes itpossible, on the one hand, to reduce the speed of incrustation as wellas the speed of wear and, on the other hand, to increase the performanceof the clutch, that is to say for identical friction surfaces of thelinings, the friction disk according to the invention exhibits anincreased lifetime and makes it possible to transmit a higher torque.

To that end, the invention proposes a friction disk, especially amotor-vehicle dry-clutch friction disk, including a support web in theform of an annular washer comprising a central portion and a outerperipheral portion subdivided into radial blades featuring a centralfixing part connected to the central portion of the web by a tangentialfold which forms the foot of the blade and allows an axial offset of thecentral fixing part with respect to the general plane of the centralportion of the web, and including friction linings on either side of theouter peripheral portion, each friction lining including an outerfriction surface and an inner fixing surface a fixing area of which isfixed onto at least one lateral fixing face of a central part of aradial blade which is offset axially towards the said friction lining,characterised in that an inner surface of a friction lining includes areduced-thickness area, or thinned area, in an area separate from thefixing areas, so as locally to reduce the axial thickness of thefriction lining, and in that at least one reinforcing element extendsfacing at least one part of a reduced-thickness area of the frictionlining in such a way as to promote the uniform distribution of thepressures over the friction surface of the lining when it is stressedaxially by a complementary plate.

By virtue of the invention, the quantity of friction material isreduced, while having good mechanical behaviour of the friction liningsby virtue of the reinforcing element, such that the solution iseconomical.

According to other characteristics of the invention:

for a good distribution of the pressures and good parallelism of thefriction linings, at least one of the radial blades features, inaddition to the central part, at least one peripheral bearing-surfacepart a lateral bearing-surface face of which comes into abutment on abearing-surface area of the inner surface of a lining which is oppositethe lining on the inner surface of which is fixed the lateral fixingface of the central part of the radial blade;

the reinforcing element extends at least partially face-to-face with alateral bearing-surface face of a peripheral part of a radial blade;

at least one reinforcing element extends substantially face-to-face withthe inner periphery of the inner surface of at least one frictionlining;

several reinforcing elements arranged between the inner surface of alining and the web of the support are linked together so as toconstitute a single element;

the single element includes a ring, the inner diameter of whichcorresponds substantially to the inner diameter of the lining facingwhich it extends, and branches which extend radially from the outerdiameter of the ring towards the outer periphery of the lining;

at least one of the branches extends face-to-face with a lateralbearing-surface face of a peripheral part of a radial blade;

the reinforcing element includes a reinforcing sector bearing against atleast one part of the reduced-thickness area, and at least one supportlug which extends axially from the reinforcing sector towards the webagainst which it bears so as to enhance the uniformity of thedistribution of the pressures over the friction surface of the frictionlining;

at least one support lug bears on the lateral face opposite the lateralfixing face of the facing blade;

at least one support lug bears on the facing lateral face of the centralportion of the radial web;

the support lug is produced from an elastic material so that itundergoes an axial deformation which is a function of the axial forceexerted, by a plate, on the friction surface of the facing lining;

at least one support lug is obtained by cutting-out and/or folding ofthe reinforcing element to which it belongs;

at least one of the linings consists of blocks or tiles delimited byedges of overall radial orientation;

at least one of the linings consists of a continuous ring.

The invention also proposes a method of manufacturing a friction lining,for a motor-vehicle clutch friction disk as described above,characterised in that it includes a stage of firing the frictionmaterial of the friction lining in a mould the area of which which is incontact with the fixing surface of the lining includes at least oneboss, so as to produce at least one reduced-thickness area or thinnedarea.

According to other characteristics of the method:

the friction material is injected into the mould;

it includes a stage of machining the fixing face of the friction liningso as to produce at least one reduced-thickness area or thinned area;

at least one reinforcing element is fixed to an element of the frictiondisk;

at least one reinforcing element is fixed to the support web;

at least one reinforcing element is fixed to the friction lining;

the friction lining is produced by overmoulding around a reinforcingelement;

at least one reinforcing element is bonded onto an element of thefriction disk;

at least one reinforcing element is riveted onto an element of thefriction disk;

at least one of the linings is bonded onto a fixing surface of a radialblade of the support web.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will becomeapparent on reading the detailed description which follows, for anunderstanding of which reference will be made to the attached drawings,in which:

FIG. 1 is a view in axial section of a friction device equipped with afriction disk;

FIG. 2 is a view in perspective of a support web of a friction disk;

FIG. 3 is an exploded view in perspective of a friction disk accordingto the state of the art;

FIG. 4 is an end view of a friction disk according to the state of theart in the new state, fitted and in a state corresponding to the openposition of the clutch;

FIG. 5 is an end view similar to that represented in FIG. 4, on a largerscale, the friction disk being represented in a state corresponding tothe closed position of the clutch;

FIG. 6 is an end view similar to that represented in FIG. 4, on a largerscale, the friction linings of the friction disk being incrusted;

FIG. 7 is an end view similar to that represented in FIG. 6, thefriction disk being represented in a state corresponding to the closedposition of the clutch;

FIG. 8 is an exploded view in perspective of a friction disk produced inaccordance with the invention;

FIG. 9 is an end view of a friction disk according to the invention inthe new state, fitted and in a state corresponding to the open positionof the clutch;

FIG. 10 is an end view similar to that represented in FIG. 9, thefriction disk being represented in a state corresponding to the closedposition of the clutch and the linings being worn;

FIG. 11 is an exploded view in perspective of a friction disk includinga reinforcing element according to a first variant of the invention;

FIG. 12 is an end view of a friction disk according to the first variantof the invention;

FIG. 13 is an exploded view in perspective of a friction disk includinga reinforcing element according to a second variant of the invention;

FIG. 14 is a sectional view along the line 14—14 represented in FIG. 13;

FIG. 15 is a sectional view along the line 15—15 represented in FIG. 13.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the remainder of the description, an axial and transverse orientationwill be used in a nonlimiting way, in accordance with the orientation ofthe rotational axis X—X of the friction disk and with a transverse planewhich is perpendicular to it. Moreover, an internal, externalorientation will be used with respect to the median transverse plane ofthe friction disk.

FIG. 1 represents a view in axial section of a friction device 10intended especially for producing a motor-vehicle clutch.

Such a device is described in the document EP-A-0 579 554, to whichreference will be made for further details.

Thus, the friction device 10 includes a first and a second coaxial part12, 14 respectively mounted mobile with respect to one another counterto circumferentially acting elastic members 16 and axially actingfriction means 18.

By way of example, the first coaxial part 12 includes two guide washers20 and 22.

A friction disk 24 is fixed, for example by riveting, onto the washer20.

The second coaxial part 14 is integral with a hub 26 intended for therotational drive of the primary shaft, with axis of rotation X—X, of agearbox which is not represented.

The friction disk 24 consists mainly of a support web 28 on the outerannular periphery of which friction linings 30 and 32 are affixed.

The web 28 is a component made of cut-out and folded thin sheet metal.

The friction linings 30 and 32 may consist of a continuous ring, or ofblocks delimited by edges of overall radial orientation.

Thus, during a clutch-engagement phase, pressure and reaction plates(not represented), which are integral with the engine flywheel, come toprogressively axially clamp the friction faces 34 and 36 of the frictionlinings 30 and 32 respectively, so as to drive the primary shaft of thegearbox in rotation by way of the friction disk 10.

FIG. 2 represents, in perspective, the support web 28 in the form of anannular washer the outer peripheral portion 40 of which here issubdivided into radial blades 42 and the central portion 46 of whichincludes clearance windows for the elastic members 16, here in the formof coil springs.

Each radial blade 42 consists of a central fixing part 44 connected to acentral portion 46 of the web 28 by a tangential fold 48 which forms thefoot of the blade 42 and which allows an axial offset of the centralfixing part 44 with respect to the general plane of the central portion46 of the web 28.

The fold 48 extends perpendicularly to the axis of radial symmetry R1 ofthe blade 42.

The plane of the central portion 46 defines a median transverse plane ofthe friction disk 24.

The web 28 here includes eight radial blades 42 which are distributed atregular angles around the X—X axis.

The radial blades 42 are alternately offset axially with respect to thecentral potion 46 in such a way that the central parts 44 define anupper plane 50 and a lower plane 52, with respect to the mediantransverse plane of the central portion 46 of the web 28, particularlyin accordance with FIG. 2.

According to a known design, known especially from the documentEP-A-0.579.554, each blade 42 is of the type called “tripod” blade.Thus, each radial blade 42 features, in addition to the central fixingpart 44, two peripheral bearing-surface parts 54.

Each tripod blade 42 features general symmetry of design with respect toa median radial axis R1.

Thus the two peripheral bearing-surface parts 54 are arrangedtangentially on either side of the central fixing part 44 which itselffeatures symmetry of design [sic] respect to the radial axis of symmetryR1.

The two peripheral bearing-surface parts 54 are flat. They are situatedin an axially offset plane. Here, they are situated in the upper plane50 when the central fixing part 44 is situated in the lower plane 52 andconversely.

The peripheral bearing-surface parts 54 of a blade 42 are connected tothe central fixing part 44 by a fold 56.

Thus, the upper 50 and lower 52 planes include the central fixing part44 of a radial blade 42 and the two pairs of peripheral bearing-surfacepart 54 of the two adjacent radial blades 42.

When the friction disk 24 is fitted, a lateral fixing face 60 of eachcentral fixing part 44 comes into contact, over a fixing area 62,delimited by dashed lines in the figures, especially in FIG. 3, with aninner fixing face 64 and 66 of the friction linings 30 and 32respectively.

The fixing of the central parts 44 and of the friction linings 30 and 32can be achieved by riveting or, advantageously, by bonding so as toreduce the inertia of the friction disk and/or allow greater wear of thefriction linings.

Moreover, lateral bearing-surface faces 55 of the peripheralbearing-surface parts 54 of a central fixing part 44 come into abutmenton bearing-surface areas 68, delimited by dashed lines in the figures,of the lining 32, 30 opposite the one onto which the correspondingcentral part 44 is fixed.

Here, the lateral bearing-surface faces 55 are simply bearing on thebearing-surface areas 68 opposite, so as to allow slipping of theperipheral bearing-surface parts 54 with respect to the correspondinglining 32, 32 during the clutch-engagement phase which causes thelinings 32, 30 to come closer together axially, and consequently causesdeformation of the web 28.

The areas of the inner fixing surfaces 64 and 66 of the friction linings30 and 32 which are neither fixing areas 62 nor bearing-surface areas 68are called free areas 70.

In order to optimise the cooling of the friction linings 30 and 32, thefriction faces 34 and 36 include grooves 71 of overall radialorientation which are oriented slightly inclined with respect to aradial direction.

FIG. 4 represents, in end view, the friction disk 24 as fitted in aposition called open position. The friction disk is in the new state,that is to say that the outer friction surfaces 34 and 36 of thefriction linings 30 and 32 are not worn.

The fixing surfaces 64 and 66 of the friction linings 30 and 32 and thelateral faces of the blades 42 which are opposite the lateral fixingfaces 60 are separated by a distance D, here initial distance D1 i.

This distance D1 i is seen again between the fixing surfaces 64 and 66of the friction linings 30 and 32 and the faces of the peripheralbearing-surface parts 54 which are opposite the bearing-surface faces55.

During a clutch-engagement phase, the pressure and reaction plates comeinto contact with the outer friction surfaces 34 and 36 of the frictionlinings 30 and 32. Each plate exerts an opposite axial force which tendsto bring the friction linings 30 and 32 axially together. As the speedsof the friction disk 24 and of the plates are not homokinetic, frictionoccurs between the surfaces in contact, which tends to drive thefriction disk 24 in rotation.

The opposed axial forces of the plates compress the friction disk 24axially in such a way as to deform the web 28, especially the folds 48and 56, as far as a clamped position in which the resisting force of theweb 28 is equal to the opposed axial forces.

FIG. 5 represents, in end view, the friction disk 24 in the new state inits clamped position.

Thus, in the course of the clutch-engagement phase, the deformation ofthe folds 48 and 56 makes it possible to provide the progressiveness ofthe clutch.

In this position, the fixing surfaces 64 and 66 of the friction linings30 and 32, and the lateral faces of the blades 42 which are opposite thelateral fixing faces 60 are separated by a final distance D1 f.

However, the use of the friction disk 24 causes wear on the frictionsurfaces 34 and 36 of the friction linings 30 and 32, as well asdeformation thereof.

The wear on the friction linings 30 and 32 is proportional to thefriction pressures exerted. Hence, the wear on the friction surfaces 34and 36 will be greater in the areas face-to-face with fixing areas 62and bearing-surface areas 68 of the fixing surfaces 64 and 66respectively.

Although the linings 30 and 32 are less worn face-to-face with the freeareas 70, they undergo deformation, that is to say that the thickness ofthe linings 30 and 32 face-to-face with the free areas 70 is deformed,pushed back overall, by the plates towards the web 28. This is thephenomenon of incrustation.

FIG. 6 represents the worn friction disk 24 in open position.

It will be observed then that the linings 30 and 32 no longer have aconstant thickness E. The areas face-to-face with the fixing areas 62and with bearing-surface areas 68 of the fixing surfaces 64 and 66respectively have a first, reduced thickness E1, and the areasface-to-face with the free areas 70 have a second thickness E2 greaterthan the first thickness E1.

Here, the dimensions of the areas face-to-face with the central parts 44are larger than those of the peripheral bearing-surface parts 54 andtheir deformation is greater.

FIG. 6 illustrates the deformation of the areas face-to-face with thefree areas 70. The distance D2 i which separates the fixing surfaces 64and 66 of the friction linings 30 and 32, and the lateral faces of theblades 42 which are opposite the lateral fixing faces 60, is reducedwith respect to the distance D1 i.

Hence, when the incrustation is greater a first threshold, or when thedistance D2 i is less than a second threshold, the progressiveness ofthe clutch is no longer regular.

In effect, two periods are produced, as described above.

In the course of the first period, the progressiveness of the clutch isregular, but the change to the second period causes a jolt whichcorresponds to the coming into contact of a free area 70 of a fixingsurface 64 or 66 with the lateral face of a blade 42 which is oppositethe lateral fixing face 60.

FIG. 7 represents the worn friction disk 24 in the clamped position ofthe clutch. The free areas 70 of the fixing surfaces 64 or 66 are incontact with the lateral face of a blade 42 which is opposite thelateral fixing face 60, the distance D2 f is zero.

If the deformation of the free areas 70 is not regular about the axisX—X, several jolts can occur, which each correspond to the coming intocontact of a free area 70 of a fixing surface 64 or 66 with a lateralface of a blade 42 which is opposite the lateral fixing face 60.

In order to augment the duration of use of the friction disk 24 duringwhich the phenomena of incrustation and of deformation do not alter theprogressiveness of the clutch, it is proposed to reduce or to thin apart of the free areas 70 so as locally to reduce the axial thickness ofthe friction linings 30, 32. The areas thus produced are calledreduced-thickness areas 72.

FIG. 8 represents such an embodiment, in exploded perspective. Thereduced-thickness areas 72 have been produced here only in the areasface-to-face with the lateral faces of the blades 42 which are oppositethe lateral fixing faces 60.

FIG. 9 is an end view of the friction disk 24, in the new state,according to the invention, in the open position of the clutch.

Advantageously, the thickness E3 of the friction linings 30 and 32 inthe reduced-thickness areas 72 and the depth P of the reduced-thicknessareas 72 are determined so that, when the linings 30, 32 have reachedtheir maximum wear, the progressiveness travel is not substantiallyaltered by comparison with the new state.

Here, although the free areas 70 face-to-face with the peripheralbearing-surface parts 54 are not reduced-thickness areas 72, theduration of use of the friction disk 24 during which the phenomena ofincrustation do not alter the progressiveness of the clutch is longerthan the lifetime of the friction disk, according to the state of theart. This is because these free areas 70 have an overhang which is verymuch less than the overhang of the free areas 70 face-to-face with thecentral parts 44. The speed of incrustation of the free areas 70face-to-face with the peripheral bearing-surface parts 54 is thereforemuch less than the speed of incrustation of the free areas 70face-to-face with the central parts 44.

The friction disk 24 also makes it possible to reduce the quantity offriction material employed for its manufacture. The mass of the frictionlinings 30 and 32 is diminished, which reduces their inertia and whichmakes it possible to increase the speed of rotation or of centrifugationof the friction disk 24. In effect, the stresses which result from therotation of the friction disk 24 are lower for the same rotationalspeed.

According to a first embodiment of the invention, in accordance withFIG. 11, the reduced-thickness areas 72 correspond to all the areas ofthe fixing surfaces 64 and 66 of the friction linings 30 and 32 whichare separate from the fixing areas 62.

In order to promote the uniform distribution of the pressures over thefriction surfaces 34 and 36 when they are stressed axially by thepressure and reaction plates, according to the invention a reinforcingelement 74 such as a branch 76 extends over the back of thereduced-thickness areas 72.

The reinforcing element 74 is manufactured from a material, such assteel or a plastic the mechanical characteristics of which are higherthan those of the friction material of the linings 30 and 32, so as toresist higher pressures without damage.

Each reinforcing element 74 may be simply interposed between a frictionlining 30 or 32 and the support web 28. It may also be fixed onto thesupport web 28 or onto a lining 30 or 32 for example by bonding,riveting or welding.

It is also possible for one of the friction linings 30 or 32 to beproduced by overmoulding around a reinforcing element 74.

As represented in the end view of the friction disk of FIG. 12, thebranches 76 advantageously extend face-to-face with a lateralbearing-surface face 55 of the peripheral bearing-surface part 54.

In order to prevent vibration from the peripheral bearing-surface parts54, it is necessary to eliminate the play between the lateralbearing-surface faces 55 and the branches 76. Hence, if it is desired tokeep the shaping of the web 28, the thickness of the branches 76 isequal to the depth P of the reduced-thickness areas 72, so that theinner face of the branch 76 comes flush with the fixing surface 64, 66of the friction lining 30, 32.

Hence, when the friction surfaces 34 and 36 are stressed axially by theplates, the branches 76, the dimensions of which are greater than thoseof the lateral bearing-surface faces 55, make it possible to distributethe forces exerted by the said bearing-surface faces 55 onto a largerarea of the friction surfaces 34 and 36.

With the forces being better distributed, that makes it possible toreduce the friction pressures between the friction surfaces 34 and 36,and the pressure and reaction plates, which has the consequence ofreducing the wear on the areas of the friction surfaces 34 and 36face-to-face with the lateral bearing-surface faces 55. The lifetime ofthe friction disk 24 is increased.

Moreover, such an embodiment makes it possible to reduce the dimensionsof the bearing-surface faces 55 and to increase those of the lateralfixing faces 60 of the blades 42. Hence, when the linings 30 and 32 arefixed onto the support web 28 by bonding, the increase in the dimensionsof the lateral fixing faces 60 makes it possible to increase the bondingsurface areas and consequently to raise the torque-handling capacitybetween the linings 30 and 32 and the web 28.

According to FIG. 11, the reduced-thickness areas 72 correspond to thewhole of the fixing surfaces 64 and 66 of the friction linings 30 and32, except for the fixing areas 62.

Hence, the reduced-thickness areas 72 include an annular area 80 whichextends from the inner periphery of the fixing surfaces 64 and 66 of thefriction linings 30 and 32 outwards as far as the fixing areas 62.Advantageously, the width L1 of the annular areas correspondssubstantially to a third of the width L2 of the friction linings 30 and32. The reduced-thickness areas 72 also include ring portions 82 whichextend between the fixing areas 62 from the annular area 80 as far asthe outer periphery of the fixing surfaces 64 and 66 of the linings 30and 32.

The reinforcing element 74 of each friction lining 30, 32 may theninclude a ring 84 the dimensions of which correspond substantially tothe annular area 80, as well as branches 76 which are arranged radiallyon either side of each fixing area 62 and which extend from the outerdiameter of the ring 84 towards the outer periphery of the correspondingfriction lining 30 and 32. Hence, a single reinforcing element 74 isaffixed to the reduced-thickness areas 72 of each friction lining 30 and32.

Hence, when the friction surfaces 34 and 36 are stressed axially by theplates, the reinforcing elements 74 make it possible to distribute theforces exerted by the bearing-surface faces 55 over a substantial areaof the friction surfaces 34 and 36. The contact pressures between thelinings 30 and 32 and plates are therefore reduced, which makes itpossible further to augment the lifetime of the friction disk 24.

Advantageously, the dimensions and especially the thickness of thereinforcing elements 74, as well as the material of which they arecomposed are chosen in such a way that when the friction surfaces 34 and36 of the friction linings 30 and 32 are worn, neither the inner facesof the reinforcing elements 74, nor the free areas 70 of the fixingsurfaces 64 and 66 are in contact with a part of the web throughout theactive clutch-engagement phase. Such an embodiment makes it possible topreserve intact the progressiveness travel and the continuity of theprogressiveness curve of the clutch throughout the lifetime of thefriction device 10.

This embodiment also makes it possible to improve the resistance of thefriction disk 24 to centrifugation.

This is because, upon rotation of the friction linings 30 and 32, themechanical stresses induced are at a maximum on the inner diameter ofthe linings 30 and 32. However, the material constituting the rings 84exhibits a mechanical strength greater than that of the materialconstituting the friction linings 30 and 32. The rings 84 than itpossible to reinforce the friction linings 30 and 32 in the areas whichare the most stressed mechanically.

It is thus possible, for identical dimensions of the linings 30 and 32,to increase the stresses due to the centrifugation, and thus to increasethe rotational speed of the friction disk 24, without risking it beingdamaged.

In order further to increase the uniformity of the distribution of thecontact pressures between the friction surfaces 34 and 36 of the linings30 and 32, the branches 76 (FIG. 13) are produced in pairs in such a wayas to form reinforcing sectors 86 which extend face-to-face with ringportions 82 of the reduced-thickness areas 72, in accordance with asecond variant represented in FIG. 13. This makes it possible to reducethe speed of wear of the friction surfaces 34 and 36 as well as thespeed of incrustation during the clutch-engagement phase.

According to this embodiment, the outer faces 88 of the reinforcingsectors 86 or body are in abutment against the face-to-face part of thereduced-thickness area 72. The reinforcing sectors 86 include supportlugs 90.

In accordance with FIG. 14, each support lug 90 extends axially overallfrom a reinforcing sector 86 towards the web 28 against which it abuts,so as to transmit the reaction forces from the web 28 towards one of thefriction linings 30 or 32, when the friction disk 24 is stressed axiallyby the pressure and reaction plates.

The support lugs 90 can be produced by cutting out and folding a part ofthe reinforcing element 74. In fact, a U-shaped cut-out is first of allformed, inclined by 90 degrees with respect to a radial direction of thereinforcing element 74. A first bend 92 is formed between the freeextremity of each of the branches of the cut-out in such a way that thefolded part extends axially towards the support web 28, then a secondbend 94 makes it possible to fold down the free end 96 of the foldedpart in a transverse plane parallel to that of the reinforcing element74.

This embodiment of the support lugs 90 makes it possible to conferelasticity on them, especially along an axial direction. Hence, when thefriction disk 24 is stressed axially by the pressure and reactionplates, they are slightly deformable axially, as a function of the axialforces exerted by the plates on the friction surfaces of the frictionlinings 30 and 32, which makes it possible to transmit the reactionforces from the web 28 towards one of the friction linings 30 or 32while ensuring the progressiveness of the clutch-engagement phase.

The axial deformation of the support lugs 90 is a function of the axialforces exerted by the plates on the friction surfaces of the frictionlinings 30 and 32.

The axial deformation of the support lugs 90 may, for example, beproportional or exponential with respect to the axial forces exerted bythe plates, that is to say that there exists a linear or exponentialrelationship between axial deformation of the support lugs 90 and theaxial forces exerted by the plates respectively.

The free extremity 96 of the support lug 90 may bear on the oppositelateral face of the lateral fixing face 60 of the blade 42 opposite, inaccordance with FIGS. 14 and 15.

In this case it may be advantageous for the radial dimension of the lug98 to correspond substantially to the radial dimension of thereinforcing sector 86 on which it is produced so as to increase thesurface area of the free extremity 96 in contact with the radial blade42 of the web 28.

The support lug 90 may also be produced in the reinforcing ring 84. Itis then referenced 100, and its free extremity 96 may then bear on theopposite lateral face of the central portion 46 of the radial web 28.

FIG. 15, which is a sectional view along the line 15—15 of FIG. 13,especially represents the support lugs 98 and 100 which are respectivelyin contact with a radial blade 42 the central portion 46 of the web 28.Thus, the lug 98 extends axially over a greater distance than the lug100.

The reaction forces from the support web 28 are then transmitted intothe areas of the friction surfaces 34 and 36 face-to-face withreduced-thickness areas 72, thus allowing a substantial reduction in theincrustation of the linings 34 and 36, as well as the uniformdistribution of the pressures over practically the whole of the frictionsurfaces 34 and 36.

Such a friction disk 24 according to the invention allows optimum use ofthe friction linings 34 and 36. This is because the friction pressuresare distributed substantially uniformly over the whole of the frictionsurfaces 34 and 36. Hence, the angular differences in the speeds of wearof the linings 34 and 36, as well as the phenomena of incrustation, aregreatly reduced.

Consequently, the speed of wear of the linings 34 and 36 is greatlyreduced, which makes it possible to augment the lifetime of the frictiondisk 24 and its ease of use for the clutch-engagement phase.

The invention also proposes a method of manufacturing a friction lining30 or 32, especially for a motor-vehicle clutch friction disk 24.

Thus, the method includes a stage of firing the friction material of thelining 30 or 32 in a mould, the area of which which is in contact withthe fixing surface 64 or 66 of the lining 30 or 32 respectively includesa boss in such a way as to form a reduced-thickness or thinned area 72.

When the friction material of the lining 30, 32 is based on fibres, suchas glass fibres, the mould may consist of two parts, each of the partsincluding a part of the imprint of the lining 30, 32. Thus, the frictionmaterial is arranged in one of the two matrices then the other matrixcomes into abutment against the first one so as to close the imprint andto form the lining 30, 32.

The friction material may also be injected directly into an imprintcorresponding to the outer shape or envelope of the lining 30, 32.

The friction material is then hardened, for example by heating beforebeing extracted from the mould.

One variant consists in producing one lining 30, 32 the fixing surface64, 66 of which is flat, then in machining this face so as to form areduced-thickness area 72.

When the friction lining 30, 32 is finished, a reinforcing element 74can be fixed to it, for example by bonding or by riveting.

The friction lining 30, 32 may also be overmoulded around thereinforcing element 74.

The bonding of the friction linings onto the central fixing area or part44 of the support web is advantageously carried out with the aid of apad. More precisely, adhesive is deposited on the parts 44 with the aidof a pad which includes an adhesive-application area the shape of whichcorresponds to the area of bonding of the lateral fixing face 60 of thecentral part 44.

In a first phase, the adhesive-application area of the pad isimpregnated with adhesive, then, in a second phase, the impregnatedadhesive-application area of the pad and the adhesive area of thelateral fixing face 60 of the central part 44 are brought into contactunder pressure so as to transfer the predetermined quantity of theadhesive from the pad onto the blade, as described in the application FR00 14929 filed on Nov. 20, 2000, to which reference should be made forfurther details.

Advantageously, the clutch includes a pressure plate in several partsbelonging to a device for compensating for the wear of the frictionlinings, called wear-take-up device.

This wear-take-up device includes, for example, a cartridge featuring aworm-screw and ratchet-wheel assembly carried by the cover which theclutch includes, as described, for example, in the document FR-A-2753503 to which reference should be made for further details.

The pressure plate therefore includes a first part forming the pressureplate and carrying a ring with ramps constituting a second part of thepressure plate.

The friction disk may belong to afriction-clutch/rotating-electric-machine assembly as described in thedocument FR-A-2 782 355; the reaction plate then being integral with therotating electric machine.

This document should be referred to for further details.

Needless to say, in a variant, the fixing of the friction linings bybonding is achieved according to the method described in the documentWO-A-98/44272, that is to say with the aid of beads of adhesive.

It will be appreciated that the fixing part of the blades is of largeextent in FIGS. 11 and 13.

This is due to the fact that the peripheral bearing-surface parts extendsymmetrically with respect to the central fixing part.

In a variant, the peripheral bearing-surface parts extend asymmetricallywith respect to the central fixing part, such that the blades can be inflag form.

Needless to say, it is possible to increase the surface area of theseperipheral bearing-surface areas. In any case, the reinforcing elementextends face-to-face with at least a part of a reduced-thickness area ofthe friction lining so as to promote the uniform distribution of thepressures over the friction surface of the lining when it is stressedaxially by a complementary plate.

It will be noted that the reinforcing element of FIGS. 11 and 13 is oflow mass. The branches 76 and the support lugs 90 alternatecircumferentially with the central parts 44.

What is claimed is:
 1. Friction disk (24), including a support web (28)in the form of an annular washer comprising a central portion (46) and aouter peripheral portion subdivided into radial blades (42) featuring acentral fixing part (44) connected to the central portion (46) of theweb (28) by a tangential fold (48) which forms a foot of the blade (42)and allows an axial offset of the central fixing part (44) with respectto the general plane of the central portion (46) of the web (28), andincluding friction linings (30, 32) on either side of the outerperipheral portion (40), each friction lining (30, 32) including anouter friction surface (34, 36) and an inner fixing surface (64, 66) afixing area (62) of which is fixed onto at least one lateral fixing face(60) of a central part (44) of a radial blade (42) which is offsetaxially towards the said friction lining (30, 32) wherein a fixingsurface (64, 66) of a friction lining (30, 32) includes areduced-thickness area (72), or thinned area, in an area separate fromthe fixing areas (62), so as locally to reduce the axial thickness ofthe friction lining (30, 32), and at least one reinforcing element (74)extends facing at least one part of a reduced-thickness area (72) of thefriction lining (30, 32) in such a way as to promote the uniformdistribution of the pressures over the friction surface (34, 36) of thelining (30, 32) when it is stressed axially by a complementary plate. 2.Friction disk (24) according to claim 1, wherein at least one of theradial blades (42) features, in addition to the central part (44), atleast one peripheral bearing-surface part (54) a lateral bearing-surfaceface (55) of which comes into abutment on a bearing-surface area (68) ofthe inner surface of a lining (32, 30) which is opposite the lining (30,32) on the inner surface (64, 66) of which is fixed the lateral fixingface (60) of the central part (44) of the radial blade (42).
 3. Frictiondisk according to claim 2, wherein the reduced-thickness areas (72)correspond to an annular area (80) which extends from the innerperiphery of the fixing surfaces (64, 66) of the friction linings (30,32) outwards as far as the fixing areas (62).
 4. Friction disk accordingto claim 3, wherein the width (L1) of the annular area (80) correspondssubstantially to a third of the width (L2) of the friction linings (30,32).
 5. Friction disk (24) according to claim 3, wherein thereduced-thickness areas (72) also include ring portions (82) whichextend between the fixing areas (62) from the annular area (80) as faras the outer periphery of the fixing surfaces (64, 66) of the frictionlinings (30, 32).
 6. Friction disk (24) according to claim 3, whereinthe reinforcing element (74) extends at least partially face-to-facewith a lateral bearing-surface face (55) of a peripheral part (54) of aradial blade (42).
 7. Friction disk (24) according to claim 6, whereinthe at least one reinforcing element (74) extends substantiallyface-to-face with the inner periphery of the inner surface (64, 66) ofat least one friction lining (30, 32).
 8. Friction disk (24) accordingto claim 7, wherein the at least one reinforcing element (74) arrangedbetween the inner surface (64, 66) of a lining (30, 32) and the web ofthe support (28) are linked together so as to constitute a singleelement (74).
 9. Friction disk (24) according to the claim 8, whereinthe single element (74) includes a ring (84) the inner diameter of whichcorresponds substantially to the inner diameter of the lining (30, 32)facing which it extends, and branches (76) which extend radially fromthe outer diameter of the ring (84) towards the outer periphery of thelining (30, 32).
 10. Friction disk (24) according to the claim 9,wherein at least one of the branches (76) extends face-to-face with alateral bearing-surface face (55) of a peripheral bearing-surface part(54) of a radial blade (42).
 11. Friction disk (24) according to claim9, wherein the thickness of the branches (76) is equal to a depth (P) ofthe reduced-thickness areas (72).
 12. Friction disk (24) according toclaim 1, wherein the reinforcing element (74) is manufactured from amaterial the mechanical characteristics of which are higher than thoseof the friction material of the friction linings (30, 32).
 13. Frictiondisk (24) according to claim 1, wherein the reinforcing element (74)includes a reinforcing sector (86) bearing against at least one part ofthe reduced-thickness area (72), and at least one support lug (90) whichextends axially from the reinforcing sector (86) towards the web (28)against which it bears so as to enhance the uniformity of thedistribution of the pressures over the friction surface (34, 36) of thefriction lining (30, 32).
 14. Friction disk (24) according to the claim13, wherein at least one support lug (98) bears on the lateral faceopposite the lateral fixing face (60) of the facing blade (42). 15.Friction disk (24) according to claim 13, wherein at least one supportlug (100) bears on the facing lateral face of the central portion (46)of the radial web (28).
 16. Friction disk (24) according to claim 13,wherein the support lug (90) is produced from an elastic material sothat it undergoes an axial deformation which is a function of the axialforce exerted, by a plate, on the friction surface (34, 36) of thefacing lining (30, 32).
 17. Friction disk (24) according to claim 13,wherein at least one support lug (90) is obtained by cutting-out and/orfolding of the reinforcing element (74) to which it belongs. 18.Friction disk (24) according to claim 1, wherein at least one of thelinings (30, 32) includes a continuous ring.
 19. Friction disk accordingto claim 1, wherein the friction linings are fixed by bonding onto thecentral fixing parts of the blades.
 20. Method of manufacturing afriction lining (30, 32), for a motor-vehicle clutch friction diskaccording to claim 1, wherein it includes a stage of firing the frictionmaterial of the friction lining (30, 32) in a mould the area of whichwhich is in contact with the fixing surface (64, 66) of the lining (30,32) includes at least one boss, so as to produce at least onereduced-thickness area (72).
 21. Method according to the claim 20,wherein the friction material is injected into the mould. 22.Manufacturing method according to claim 20, wherein at least onereinforcing element (74) is fixed to an element of the friction disk(24).
 23. Manufacturing method according to the claim 22, wherein atleast one reinforcing element (74) is fixed to the support web (28). 24.Manufacturing method according to claim 22, wherein at least onereinforcing element (74) is fixed to the friction lining (30, 32). 25.Manufacturing method according to the claim 24, wherein the frictionlining (30, 32) is produced by overmoulding around a reinforcing element(74).
 26. Manufacturing method according to claim 22, wherein at leastone reinforcing element (74) is bonded onto an element of the frictiondisk (24).
 27. Method of manufacturing a friction lining (30, 32), for amotor-vehicle clutch friction disk (24) according to claim 1, wherein itincludes a stage of machining the fixing face (64, 66) of the lining(30, 32) so as to produce at least one reduced-thickness area (72).